Watch all imported files in linked npm packages on server.

tools/fs/optimistic.js

@@ -74,7 +74,7 @@ function makeOptimistic(name, fn) {
   return Profile("optimistic " + name, wrapper);
 }
 
-function shouldWatch(path) {
+export const shouldWatch = wrap(path => {
   const parts = path.split(pathSep);
   const nmi = parts.indexOf("node_modules");
 
@@ -113,7 +113,7 @@ function shouldWatch(path) {
   // instead we rely on dependOnNodeModules to tell us when files in
   // node_modules directories might have changed.
   return false;
-}
+});
 
 function maybeDependOnNodeModules(path) {
   if (typeof path !== "string") {

tools/isobuild/import-scanner.js

@@ -28,6 +28,7 @@ import {
   optimisticReadFile,
   optimisticStatOrNull,
   optimisticHashOrNull,
+  shouldWatch,
 } from "../fs/optimistic.js";
 
 import Resolver from "./resolver.js";
@@ -557,11 +558,19 @@ export default class ImportScanner {
       // Append this file to the output array and record its index.
       this._addFile(absImportedPath, depFile);
 
+      // On the server, modules in node_modules directories will be
+      // handled natively by Node, so we don't need to build a
+      // meteorInstall-style bundle beyond the entry-point module.
       if (! this.isWeb() &&
-          depFile.installPath.startsWith("node_modules/")) {
-        // On the server, modules in node_modules directories will be
-        // handled natively by Node, so we don't need to build a
-        // meteorInstall-style bundle beyond the entry-point module.
+          depFile.installPath.startsWith("node_modules/") &&
+          // If optimistic functions care about this file, e.g. because it
+          // resides in a linked npm package, then we should allow it to
+          // be watched by including it in the server bundle by not
+          // returning here. Note that inclusion in the server bundle is
+          // an unnecessary consequence of this logic, since Node will
+          // still evaluate this module natively on the server. What we
+          // really care about is watching the file for changes.
+          ! shouldWatch(absImportedPath)) {
         return;
       }